Table saws have a rotating saw blade extending through their upper surface for cutting work pieces positioned on the upper surface of the table saw. Typically, table saws are used for cross cutting, or cutting transverse to the length of the work piece, bevel cutting, which refers to cutting at an angle to the length of the work piece, and rip cutting, which refers to longitudinal cutting along the length of the work piece. For cross cutting and bevel cutting, an angularly and laterally adjustable fixture or fence is used, whereas for rip cutting, a separate rip fence must be used to hold the work piece in the desired position for the longitudinal or rip cutting that is to be performed.
The claimed invention is directed to a new and improved anti-kick rip fence for table saws and to an anti-kick rip fence safety guide for attachment to the rip fence of existing saws. Prior art rip fences work well to provide a linear guide fence along which a work piece is slideable relative to the rotatable saw blade to cut the work piece. Unfortunately, prior art rip fences can cause dangerous work piece kickback incidents.
Table saw blades rotate at high speed into the direction of the cut. The circular steel saw plate, which gives the blade its size and shape as well as fixing it to the motor arbor, is also the surface onto which the cutting teeth are attached. The “kerf” of a blade is the amount of material it removes from the stock, or, in other words, the width of the cutting teeth (and therefore, the cut). The saw plate thickness is less than that of the teeth, which provides relief between the stock and the blade.
No matter what profile the blade teeth have, the kerf will be wider than the saw plate. This allows the plate to run free within the kerf already cut into the stock as it is passed through the blade. If the saw plate were as wide as the cutting teeth, then the whole face of the saw plate would be in friction contact with the sides of the cut.
Once the stock has passed the “center” of the saw blade and therefore the center of rotation of the saw blade, the “back” of the blade has the tendency to lift the work piece upwards as soon as it overcomes the weight of work piece and any downward force applied to it. Once the weight of the work piece has been overcome, the friction of the blade upon the stock gains enough grip on the side of the work piece to propel the work piece in the direction of travel of the blade, which is unfortunately towards the operator.
As indicated above, saw plates are not as wide as their cutting teeth. Therefore, in a perfect setup wherein the rip fence is perfectly aligned with the saw blade, the saw will run freely within the width of the kerf of the cut and the work piece will never kick back. Unfortunately, it can be difficult to place the rip fence perfectly relative to the saw. For example, if the rip fence is skewed towards the saw, the work piece will become pinched between the saw and the rip fence and greatly increase the chance of a kickback incident.
Riving knives can also reduce the chances of a kickback incident. The purpose of the riving knife is to prevent sideways pressure on the blade from stock which is passing through. In order to work properly, the riving knife must be no thicker than the blade kerf and be adjusted to be in line with the blade. If not adjusted properly, the riving knife can actually cause further binding which can also lead to a kickback incident.
Therefore, what is needed is a simple and inexpensive rip fence or an attachment to a rip fence that is designed to reduce binding between the rip fence and the saw blade.